Evaluating the Efficacy and Safety of a Sequencing Schedule of Cobimetinib Plus Vemurafenib Followed by Immunotherapy With an Anti- PD-L1 Antibody in Patients With Unresectable or Metastatic BRAF V600 Mutant Melanoma

At this time there is no experience concerning the sequencing strategy when using the two effective therapeutical approaches as targeting the Ras/Raf signalling pathway by BRAF and MEK inhibition or targeting immunologic checkpoint control with an antiPD-L1 antibody. This is a prospective, open, multicenter, randomized phase II study in patients with unresectable or metastatic BRAFV600 mutant melanoma. In this study the scheduling of the treatment with a combined BRAF/MEK inhibition and the treatment with an anti-PD-L1 antibody will be assessed. After a 3 months run-in period with vemurafenib and cobimetinib, all patients who did not show disease progression or treatment interruption for more than 28 days during run-in phase will be randomized in a 1:1 ratio: * either to proceed vemurafenib and cobimetinib until disease progression and subsequently cross-over to atezolizumab treatment until disease progression (Arm A). * or to receive the anti-PD-L1 antibody atezolizumab until disease progression and subsequently cross-back to vemurafenib and cobimetinib until disease progression (Arm B). In a translational research program tumor tissue, blood plasma and peripheral blood mononuclear cell will be analyzed to evaluate the biologic effects of treatment sequence on the molecular profile and biomarker expression in tissue and plasma.